IMPROVED PILE DRIVER

Abstract: An improved pile driver, for use in hazardous gas environments, which comprises: a housing having a hammer mounted therein for reciprocating movement, the housing having a shroud extending over the hammer's head and to amount over a pile or pile chaser, thereby forming an impact chamber around the point of impact of the hammer head upon the pile or pile chaser, wherein gas sampling and analysis means are provided to sample and analyse the gas within the impact chamber during operation to detect any changes in the gas composition which may reflect influx of hazardous gases.

Description: IMPROVED PILE DRIVER Field of the Invention The present invention relates to an improved pile driver primarily for use around oil or gas wells and in other hazardous gas environments. Background to the Invention Pile driving is applied widely throughout the oil and gas industries for anchoring rig structures in the ground both on and offshore and for forming and lining the wells. As with other aspects of the oil and gas industry, the safety of operational procedures and equipment used for pile driving in the vicinity of the oil or gas well is of paramount importance. Pile driving in the vicinity of an oil or gas well is a particularly hazardous operation. In an environment prone to build up of combustible and explosive gases, sparks and frictional heat are generated by the hammer as it strikes the pile or pile chaser with a high energy impact and rapidly compressing gases in the impact chamber. The common place provision of a shroud extending from the housing of the pile driver to centralise the hammer of the pile driver over the pile exacerbates the problem by providing a partially enclosed chamber into which surrounding environmental gases are alternately sucked as the hammer reciprocates. A particularly problematic consequence of the hazardous nature of pile driving in this environment is that, although frequently necessary or strategically desirable, a fresh well cannot be driven in the immediate vicinity of an operating well, eg within 2.5m of the well, without temporarily shutting down the existing well with resultant productivity loss from that well. It is a general objective of the present invention, amongst others, to overcome this particular problem. Summary of the Invention According to a first aspect of the present invention, there is provided a pile driver which comprises: a housing having a hammer mounted therein for reciprocating movement, the housing having a shroud extending over the hammer's head and to mount over a pile or pile chaser, thereby forming an impact chamber around the point of impact of the hammer head upon the pile or pile chaser, wherein gas sampling and analysis means are provided operatively linked to the housing to sample and analyse the gas within the impact chamber during operation to detect any changes in the gas composition which may indicate influx of hazardous gases and to generate a signal indicative thereof. Preferably the gas sampling and analysis means are operatively linked to the housing by a pipe mounted to the housing and opening into the impact chamber. This enables the relatively delicate gas analysing means to be located remote from the hammer during its operation. Preferably, the gas sampling and analysis means are, furthermore, operatively linked to an automatic shut-off control to inactivate the hammer in response to the signal. Suitably, the gas sampling and analysis means are operatively linked to an alarm system to provide a visible or audible alarm response to the signal. The apparatus may be further refined by providing that the shroud has an inlet for supply of a substantially inert gas into the impact chamber and an outlet to allow efflux of the gas from the impact chamber, and valve means within the outlet for substantially preventing influx of external gases during operation of the pile -εr enabling maintenance of a substantially inert gas atmosphere within the impact chamber during operation of the tool, while not significantly impeding movement of the hammer. Particularly advantageously, the outlet comprises the opening of the shroud which fits over the pile or pile chaser. Preferably, the pile driver further comprises a supply of substantially inert gas and gas supply control means to supply the substantially inert gas to the impact chamber continuously, intermittently or in response to the signal. Preferably, the pile driver has an operation control means having feedback control means to provide closed loop negative feedback control of the power input to the hammer and which comprises velocity sensors associated with the hammer to sense the velocity of the hammer in operation from which the actual kinetic energy imparted to the hammer is computed and compared with a desired target level, the operation control means responding to the difference between the actual kinetic energy and the target kinetic energy level to adjust the power supply to the hammer to compensate for the difference. The pile driver suitably has a jiggling control means whereby the power to the hammer may be restricted to a low level whereby the hammer does not impart sufficient energy to an anvil upon which it acts, in use, to significantly dislodge the hammer from the anvil upon recoil. Where the pile driver has said jiggling control means, the power supplied to that hammer is suitably restricted to below the level whereby the hammer would be raised far enough to enable the velocity sensors to sense the velocity of the hammer. By way of further improvement tc the safety of operation of the pile driver, said pile driver suitably has a pneumatic actuator which switches the direction of movement of the hammer for its reciprocation and is, furthermore, suitably controlled by an intrinsically safe solenoid operated pneumatic valve which is driven through Intrinsic Safety barriers, preferably of spool valve type. Brief Description of the Drawings A preferred embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein; Figure 1 is a schematic longitudinal sectional view of a pile driver embodying the present invention; Figure 2 is view similar to that of Figure 1, with the piston in its lowered position; Figure 3 is a view of the piston in the raised position; Figure 4 is a schematic representation of the control system; Figure 5 is a more detailed block diagram of the control system; Figure 6 is a line diagram of the control system safety components; Figure 7 shows the air sampling system for gas detection; and Figure 8 shows the operational configuration of the pile driver in position on the rig floor. Description of the Preferred Embodiment As shown in Figure 1, the pile driver comprises a hydraulically powered piston 1 and an associated hammer 2 which are longitudinally slidably mounted within an elongate housing 3 having at one end nitrogen-charged accumulators 4 and at the other end an opening through which the head 5 of the hammer 2 projects to impact upon an impact plate, or anvil, 6. The end of the pile driver housing 3 nearest to the hammer head 5 extends to form a shroud 7 which encloses the impact plate, or anvil, 6 and fits over one end of a pile 10 to be driven, forming a substantially enclosed impact chamber 8. The pile 10 is held substantially centrally within the shroud 7 by shims 9. Comparison of Figures 2 and 3 shows how the piston 1 moves within the housing 3. To improve safety of the pile driver for operation in hazardous, inflammable, gas environments, those elements of the system which provide the electronic control of the tool and which are mounted to the tool (velocity sensors 13 and solenoids 26) are suitably all Intrinsically Safe (IS) components utilising low electrical energy levels and supplied with low energy via intrinsically safe control lines 24, o from an explosion proof control box 14 through intrinsic safety barriers. By definition, the energy levels supplied are so low that should a spark occur this would be insufficient to ignite any surrounding combustible gases. Intrinsic barriers also provide electrical isolation from earth. Should an explosion occur within the control box 14 it will not be able to escape. The points of exit and entry of the intrinsically safe control lines 24, 4o to and from the control box 14 are provided with barrier glands of epoxy resin to prevent transference of any explosion from within the box 14. The high powered solenoid coil conventionally used to initiate the switch in direction during hydraulically powered reciprocating motion of the piston 1 is replaced by a pneumatic actuator 12 controlled by an Intrinsically Safe solenoid-operated pneumatic spool valve. The spool valve is supplied with compressed air from the rigs air supply (not shown) the supply of which is controlled at the tool by the IS solenoids 26. The pneumatic actuator 12 is suitably external of the hammer 2 to overcome, the problem of space limitation within the tool. The conventional sensors used to determine the operational displacement of the piston are suitably replaced with sensors 13 which are certified Intrinsically Safe and also driven through intrinsic safety barriers. The control box 14 containing the main switch controls and CPU for the pile driver is suitably mounted in an explosion-proof housing. In use, the control box 14 is placed remote from the hammer 2 due to the extreme vibration in the vicinity of the working hammer. The operation of the hammer is controlled in a feedback mechanism and monitors gas composition and pressures within the impact chamber 8. To this latter end, a gas sampling and analysis probe 15 comprising a flexible pipeline mounted at one end to the shroud 7 is provided opening into the chamber 8 directing gas samples from within the chamber to a detector and analyser 25 built in or added onto the control box 14. Referring to Figure 8, the detector and analyser 25 receives air samples supplied by the pipeline 15 which is drawn into the detector by use of a Venturi vacuum ejector pump 28 which exhausts mixed air and gas to atmosphere. This pump 28 has no working parts and is therefore not prone to frictional heat or spark generation. The pump is operated through supply of air from the rig air supply via a filter/regulator 29 which has its own associated control circuit 30. To ensure that air flow through the detector 25 occurs upon demand and is not obstructed an air flow detector orifice 31 and an IS flow detection circuit 33 receiving air via a low pressure diaphragm 34 provided. Further precautionary measures include provision of an over pressure protection device 32. In order that the operation of the vacuum pump drawing air through the detector 25 does not occur when the pipeline 15 is detached from the shroud 7 of the tool potentially blocking and contaminating the equipment, a pneumatic conditioning box 18 is provided having an IS solenoid valve 35 and an air flow switch 36. An overview of the control system is shown in Figure 4. It consists of four main sections (further details shown in Figure 6): 1. Explosion-proof (EExd) control box 14 with integral/securely close coupled EExd gas detector and analyser 25 and associated vacum pump 28 to draw the gas samples, the whole being, powered at input 17 by the rig power supply; 2. Pneumatic conditioning box 18 (shown in figures 5 and 6) with EExi solenoid valve 35 and air flow switch 36 to control operation of the vacuum pump 28;. 3. Hammer mounted EExi control solenoids 26 and EExi sensors 13; and 4. Remote control pod 19 containing the emergency stop switch 37, energy supply increase switch 38 and energy supply decrease switch 39. The hammer is suitably programmed so that it will not operate until the two set up procedures described have been followed. Initial Set-Up Computer software allows the operator to check that all elements of the control and safety system are operating correctly. By using the front panel controls on the EExd control box 14 it is possible to verify the operation of: hammer hydraulic pressure line control valve; hammer hydraulic return line control valve; gas sniffer vacuum pump control valve; remote emergency stop; energy increase; energy decrease; and local emergency stop. When the operator is satisfied that all elements of the control system are operating correctly, the Gas Sniffer set-up cycle is proceded to. Gas Sniffer Set-up Cycle The gas detector ("sniffer") set-up has two stages: 1. The solenoid valve 35 controlling the air sampling vacuum pump is operated and air flow must be detected and remain stable during the set-up cycle. 2. Once stable air flow has been observed, the gas detector must indicate a safe condition for a continuous period of 30 seconds. If at any time during this warm up period, the airflow is lost or hazardous gas is detected, then the internal time is reset to 30 seconds and begins the countdown to zero again. Once a safe and stable warm up is completed, the normal running mode is activated and the hammer can now be operated, provided all other safety checks have been satisfied. As described previously, the system is set up to operate on a negative feedback control basis whereby the sensors 13 transmit information back to the control system in the control box 14 which is responded to by increasing or decreasing the power supplied to the piston 1 to bring its action closer into line with the desired target level for energy imparted to the anvil and pile. In a preferred embodiment, an additional mode of operation is provided, whereby the piston 1 is powered at such a low level that it does not rise past sensors 13 and does not impart sufficient energy to the piston upon recoil that it separates from the anvil. This produces a jiggling motion which is useful for displacing the pile through relatively small distances, minimising air compression and spark generation and any risk of dislodgement of the tool during use. This is a particular benefit when initiating the pile driving or when sudden changes in the resistance of the ground into which the pile is being driven are experienced. In one option the forward most end of the shroud 7 is provided with a partial gas seal, or valve, 20 occluding the annular space between the internal bore of the shroud 7 and tne circumferential surface of the pile 10. The valve 20 is suitably an elastomeric/neoprene diaphragm arranged to permit efflux of gas from the impact chamber 8 while preventing influx of gases from the environment surrounding the shroud 7 into the chamber 8, even during the retraction of the hammer 2. In a preferred embodiment, the valve 20 closes when the pressure within the chamber 8 falls below 50 millibars. An inlet pipe 21 is provided opening into the shroud 7 to supply substantially inert gas such as compressed air or nitrogen from a gas canister or other source 22 to purge the atmosphere within the chamber 8 of any combustible gases that might be present. Supply of the inert gas through the valve 23 to the impact chamber is suitably controlled by the control system. The gas sampling and analysis probe 15 hence also transmits input signals to the purge control valves 23. Should any potentially adverse alteration in the gas composition within the impact chamber 8 be detected by the gas sampling probe 15, the purge control unit 21 will increase, or initiate, further supply of the inert gas or comj- essed air to the impact chamber 8. If a sudden and sharp rise in potentially combustible gas content is detected, an automatic shut down system will prevent further operation of the hammer until the combustible gases have been fully purged.

Claims: Claims 1. A pile driver which comprises: a housing having a hammer mounted therein for reciprocating movement, the housing having a shroud extending over the hammer's head and to mount over a pile or pile chaser, thereby forming an impact chamber around the point of impact of the hammer head upon the pile or pile chaser, wherein gas sampling and analysis means are provided operatively linked to the housing to sample and analyse the gas within the impact chamber during operation to detect any changes in the gas composition which may indicate influx of hazardous gases and to generate a signal indicative thereof. 2. A pile driver as claimed in Claim 1, wherein the gas sampling and analysis means are operatively linked to the housing by a pipe mounted to the housing and opening into the impact chamber. 3. A pile driver as claimed in Claim 1 or Claim 2, wherein the gas sampling and analysis means are, furthermore, operatively linked to an automatic shut-off control to inactivate the hammer in response to the signal. 4. A pile driver as claimed in Claim 1, 2 or 3 wherein the gas sampling and analysis means are operatively linked to an alarm system to provide a visible or audible alarm response to the signal. 5. A pile driver as claimed, in any of Claims 1 to 4, which has a venturi vacuum ejector pump to draw the gas samples from the impact chamber. 6. A pile driver as claimed in any preceding Claim, wherein the shroud has an inlet for supply of a substantially inert gas into the impact chamber and an outlet to allow efflux of the gas from the impact chamber, and valve means within the outlet for substantially preventing influx of external gases during operation of the pile driver enabling maintenance of a substantially inert gas atmosphere within the impact chamber during operation of the tool, while not significantly impeding movement of the hammer. 7. A pile driver as claimed in Claim 6 and any other Claim which further comprises a supply of substantially inert gas and gas supply control means to supply the substantially inert gas to the impact chamber continuously, intermittently or in response to the signal. 8. A pile driver as claimed in any preceding Claim and which has an operation control means having feedback control means to provide closed loop negative feedback control of the power input to the hammer and which comprises velocity sensors associated with the hammer to sense the velocity of the hammer in operation from which the actual kinetic energy imparted to the hammer is computed and compared with a desired target level, the operation control means responding to the difference between the actual kinetic energy and the target kinetic energy level to adjust the power supply to the hammer to compensate for the difference. 9. A pile driver as claimed in any preceding Claim and which has a jigging control means whereby the power to the hammer may be restricted to a low level whereby the hammer does not impart sufficient energy to an anvil upon which it acts, in use, to significantly dislodge the hammer from the anvil upon recoil. 10. A pile driver as claimed in Claim 9 and any other claim, wherein the power supplied to that hammer is restricted to below the level whereby the hammer would be raised far enough to enable the velocity sensors to sense the velocity of the hammer. 11. A pile driver as claimed in any preceding Claim, wherein, the pile driver has a pneumatic actuator which switches the direction of movement of the hammer for its reciprocation. 12. A pile driver as claimed in Claim 11, wherein the pneumatic actuator is controlled by an intrinsically safe solenoid operated pneumatic valve which is driven through Intrinsic Safety barriers. is controlled by an intrinsically safe solenoid operated pneumatic valve which is driven through Intrinsic Safety barriers. 13. A pile driver substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: CLAY ROBERT ALBERT, CLAY, ROBERT, ALBERT
Applicants: CLAY ROBERT ALBERT, PARAMODE LTD, CLAY, ROBERT, ALBERT, PARAMODE LIMITED
Application year: 1994
Main classification: E02D7
IPC codes: E02D13